The River Medway is polluted with dangerous chemicals which cause cancer, breathing problems and severe harm to insects and wildlife, testing reveals.

Toxic chemicals used in industrial processes, the paving of roads and in pet flea-repellents have found their way into the waters of the Medway, posing a significant risk to humans and animals alike.

Data from the Environment Agency, analysed by WATERSHED Investigations, has shown the River Medway contains substances such as 1,4-dichlorobenzene, which is deemed to be very toxic to aquatic life with long-lasting effects, and even believed to cause cancer.

Additionally found was chrysene, which is a component in coal tar, creosote and asphalt, which is extremely toxic and is believed to cause long-term genetic defects for fish, insects, and aquatic animals.

Levels of naphthalene, cyclohexanone, N,N-diethyl-m-toluamide, pyrene, and fluoranthene are also among the cocktail of chemicals which pose risks to wildlife and humans who enjoy the river.

Each poses various threats to humans, some causing irritation of the skin and eyes, while all are dangerous for the organisms which rely on the river for their habitat.

The largest contaminant found in the sampling was caffeine, which was found at a concentration of 0.09 micrograms per litre (ug/l).

While this might sound small, caffeine can have detrimental impacts on aquatic wildlife, including affecting reproduction and development, and can be deadly to insects.

While other chemicals are likely to have entered the river through rainfall run-off, caffeine is likely entering the waters via sewage treatment after being ingested by humans.

Angus Kennedy is the rowing coach at Rochester Rowing Club, which uses the Medway for training.

He says the findings are incredibly concerning for people using the waters on a regular basis, and thinks it might put people off joining the club.

He said: “It used to be people not being able to swim was our biggest safety issue, but now our biggest safety issue is people swallowing water if they fall in.

“We’re really unhappy about how filthy the river has become - the rubbish coming down all the time, you see bottles, canisters, all sorts whenever you row.”

Mr Kennedy had a campaign to try and put together a senior rowing team to take to Henley, but said it was hard to convince people to get involved - in part because of the state of the waters.

“The junior squad has a lot of members, but as far as the senior squad is concerned, I found it very difficult to get members and it may be because people are just looking at this water and thinking ‘I'm not rowing on that because it’s filthy’.

“I think it should be a criminal offence to put toxic chemicals in the water, because you're potentially causing people illness and potentially killing some people.

“Anyone who pollutes our rivers and waterways with nasty chemicals and sewage should be locked up for a long time.

“Fines aren’t enough - people hide behind these big companies who take the financial hit, if they were facing jail time I’m certain this disgraceful dumping of dangerous stuff would stop immediately.

“All people who use the river, swimmers, rowers, boaters, waterskiers, they’re all at risk and seem to be powerless in this.”

This follows the findings that more than 600 million litres of sewage was dumped into the waters around Medway in 2022.

WATERSHED Investigations is an independent journalism organisation which aims to raise awareness of the state of Britain’s waterways through reports.

They have produced an interactive map which displays data from across the country, showing what chemicals have been found in which waterways.

An Environment Agency spokesperson said: “The River Medway has a history of intense industrial use and was historically contaminated with many compounds.

“Our routine monitoring tracks the legacy of this pollution and will pick up any new contaminates entering the waterways.

“Some compounds such as chrysene have many sources including the burning of coal, petrol and was a primary constitute of creosote. Naphthalene similarly to chrysene was a by-product of coke production and was used in many industries for dye, insecticides, plasticizers and to sterilise soils against fungi.

“Many of these processes are either banned or reduced, however there will be a historical footprint for many years as the chemicals leach from the soil or are released from sediment in the waterbody.

“Strict regulation of industry backed up by monitoring will continue to reduce the concentration of these chemicals into our rivers and sea.”